1. Field of the Invention
The present invention relates to a process for producing a substrate including a plating layer and to a plating apparatus for forming a plating layer of a substrate; and, more particularly, to a process for producing a substrate including a base-metal plating layer and to a plating apparatus for forming a base-metal plating layer.
2. Description of the Related Art
Conventionally, a substrate including a layer plated with a base metal such as Ni has been known. For example, in a wiring substrate on which an IC chip is to be provided, usually, an Ni-plating layer (base-metal plating layer) is formed on a connection terminal formed from Cu, and an Au-plating layer is formed on the Ni-plating layer in order to prevent oxidation of the Ni-plating layer.
Such a plating layer of a wiring substrate is formed as follows. A wiring substrate on which an Ni-plating layer is to be formed is subjected to Pd activation treatment before plating, and then the wiring substrate is washed with water.
After washing with water, the wiring substrate is immersed for a predetermined period of time in an Ni-plating solution contained in an Ni-plating tank, to thereby form on a connection terminal of the wiring substrate an Ni-plating layer of predetermined thickness.
Specifically, as shown in FIG. 6, after being washed with water, wiring substrates 101 are transferred horizontally to a position above an Ni-plating tank 111 by means of a transfer mechanism 103. The transfer mechanism 103 includes a rack 105 for holding a number of the wiring substrates 101, a vertical transfer mechanism 107 for transferring the rack 105 vertically, and a horizontal transfer mechanism 109 for transferring the rack 105 horizontally.
Subsequently, from the position above the Ni-plating tank 111, the rack 105 is moved downward by means of the vertical transfer mechanism 107, and the rack 105 (along with the wiring substrates 101) is immersed for a predetermined period of time in an Ni-plating solution contained in the Ni-plating tank 111.
After a n Ni-plating layer is formed on each of the wiring substrates 101, the rack 105 is removed from the Ni-plating tank 111 by means of the vertical transfer mechanism 107. Subsequently, the rack 105 is transferred, by means of the horizontal transfer mechanism 109, to a position above a washing tank 113 containing washing water.
Thereafter, the rack 105 is moved downward by means of the vertical transfer mechanism 107, and the rack 105 is immersed f or a predetermined period of time in the water contained in the washing tank 113, to thereby wash the wiring substrates 101.
After the substrates are washed, the rack 105 is removed from the washing tank, and transferred to a position above an Au-plating tank (not illustrated) containing an Au-plating solution. Subsequently, the rack 105 is immersed for a predetermined period of time in the Au-plating solution contained in the Au-plating tank, to thereby form an Au-plating layer on the Ni-plating layer formed on each of the wiring substrates 101.
Thereafter, the rack 105 is removed from the Au-plating tank, transferred to the subsequent washing tank (not illustrated) containing washing water, and immersed in the water contained in the washing tank, to thereby wash the wiring substrates 101. Subsequently, the wiring substrates 101 are dried. Thus, the Ni-plating layer and Au-plating layer are formed on a connection terminal of each of the wiring substrates 101.
3. Problems to be Solved by the Invention
However, in the aforementioned production process, a certain time elapses from the time the rack 105 (along with the wiring substrates 101) is removed from the Ni-plating tank 111 until the rack 105 is immersed in the water contained in the washing tank 113. In addition, when the Ni-plating layer is formed, the wiring substrates 101 are heated, since the Ni-plating solution contained in the Ni-plating tank 111 is heated at about 70-90xc2x0 C. Therefore, during transfer of the wiring substrate 101, the Ni-plating layer formed on the wiring substrate 101 is exposed to air, while the temperature of the layer is maintained at a high level.
Consequently, during transfer of the wiring substrate 101, the Ni-plating solution which remains on the substrate may oxidize, leading to problems such as blackening of the surface of the Ni-plating layer and formation of a thin oxidation film. In such cases, when solder bumps are formed on the connection terminal of the wiring substrate 101 on which the Ni-plating layer has been formed, the bonding strength between the Ni-plating layer and the solder may be lowered, thereby lowering the bonding reliability.
In view of the foregoing, an object of the present invention is to provide a process for producing a substrate which prevents oxidation of residual Ni-plating solution and accompanying problems, including discoloration of a base-metal plating layer and lowering of bonding strength; and a plating apparatus therefor.
The present invention achieves the above object by providing a process for producing a substrate including a base-metal plating layer, which process comprises an immersion step for immersing a substrate in a plating solution contained in a plating tank, to thereby form a base-metal plating layer on a substrate; a washing step which comprises removing the substrate from the plating tank, transferring the substrate to a washing tank, and washing the substrate; and a cooling step which comprises applying cooling liquid to the substrate during at least a portion of the period during which the substrate is being transferred to the washing tank after completing the immersion step, to thereby cool the substrate.
According to the present invention, while the substrate which has undergone the immersion step is removed from the plating tank and is being transferred to a position where the washing step is carried out, cooling liquid is applied to the substrate, to thereby cool the substrate. When cooling liquid is applied during the substrate transfer step, the period of time during which the heated substrate (as heated in the plating tank) is exposed to air is shortened.
Consequently, during transfer of the substrate, plating solution which remains on the substrate is less likely to oxidize, thereby making the substrate less prone to accompanying problems, including blackening of the surface of the plating layer and formation of a thin oxidation film. Therefore, when solder bumps are formed on the plating layer, the bonding strength between the plating layer and the solder is not lowered, and bonding reliability can be enhanced.
The cooling liquid is not particularly limited, so long as the solution can cool the substrate. For example, the cooling liquid may be water, pure water, a plating solution, or a washing solution. The temperature of the cooling liquid is not particularly limited, so long as the cooling liquid can cool the substrate to a temperature so as to suppress reaction of the plating solution which remains on the substrate. The temperature of the cooling liquid may be ambient temperature. The cooling liquid itself may be cooled. Alternatively, the cooling liquid may be heated to some extent, so long as the temperature of the cooling liquid is lower than that of the plating solution contained in the plating tank.
The cooling step may be carried out continuously over the entire substrate-transfer period during which the substrate is transferred from the plating tank to the subsequent washing tank, or during a portion of the transfer period.
In the cooling step of the aforementioned process for producing a substrate, preferably, the cooling liquid is applied to the substrate while the substrate is being removed from the plating tank, to thereby cool the substrate.
In this case, the substrate is cooled simultaneously with removal from the plating tank, thereby minimizing the time during which the plating layer of the heated substrate is exposed to air at high temperature during transfer of the substrate from the plating tank to the subsequent washing tank.
Consequently, the occurrence of problems including oxidation of the surface of the plating layer can be more reliably prevented, and thus a highly reliable substrate can be produced.
In the cooling step of the aforementioned processes for producing a substrate, preferably, the cooling liquid is sprayed obliquely upward, and, when falling as a result of spraying, the cooling liquid is applied to the substrate from above the substrate. When the cooling liquid is sprayed in such a manner, the cooling liquid is easily atomized in air. Therefore, the cooling liquid can be uniformly applied to the substrate, to thereby cool the substrate uniformly.
Moreover, the temperature of the cooling liquid is preferably ambient temperature. This is because, when at ambient temperature, the cooling liquid can cool the substrate satisfactorily, thereby preventing problems including oxidation of the plating layer. In addition, employing a cooling liquid of ambient temperature obviates a step specifically for cooling or heating the cooling liquid, and thus costs incurred by the cooling step can be reduced.
In the aforementioned processes for producing a substrate, the cooling liquid is preferably pure water.
In a preferred embodiment of the present invention, pure water is used as the cooling liquid. Therefore, an apparatus for applying the cooling liquid to the substrate can be simplified, as compared with the case in which a plating solution, a washing solution, or a similar solution is used as the cooling liquid. Moreover, in the case in which pure water is used as the cooling liquid, when the cooling liquid is applied to the substrate to thereby cool the substrate above the plating tank, and the cooling liquid falls from the substrate into the tank and is mixed with the plating solution, the plating solution is not adversely affected. Similarly, use of pure water as the cooling liquid is advantageous, because when the cooling liquid is applied to the substrate to thereby cool the substrate above the washing tank, and the cooling liquid falls from the substrate into the tank, the washing solution in the tank is not adversely affected. In addition, even when the cooling liquid falls from the substrate onto the floor, the cooling liquid is relatively easily disposed of.
In the aforementioned processes for producing a substrate, the base-metal plating layer is preferably an Ni-plating layer predominantly containing Ni.
According to the present invention, an Ni-plating layer predominantly containing Ni is formed in the immersion step. When the Ni-plating layer is formed on the substrate, while the substrate is transferred from the plating tank to the washing tank, the surface of the Ni-plating layer is easily oxidized, particularly at high temperature. Therefore, as described above, when the cooling step is carried out during transfer of the substrate, and the substrate is cooled by the cooling liquid, occurrence of problems, including oxidation of the surface of the Ni-plating layer, can be effectively prevented.
The present invention also provides a plating apparatus for forming a base-metal plating layer on a substrate, which comprises a plating tank for storing a plating solution; a washing tank for storing a washing solution; transfer means for removing from the plating tank a substrate on which a base-metal plating layer has been formed, transferring the substrate to the washing tank, and immersing the substrate into a washing solution contained in the washing tank; and cooling means for applying a cooling liquid to the substrate removed from the plating tank.
According to the present invention, the plating apparatus includes the plating tank, the washing tank, the transfer means, and the cooling means. When the substrate on which the base-metal plating layer has been formed is removed from the plating tank, the cooling means allows the cooling liquid to be applied to the substrate so that the substrate is cooled.
Thus, when the substrate is cooled while being removed from the plating tank, during transfer of the substrate from the plating tank to the washing tank, the time during which the heated substrate is exposed to air at high temperature is shortened. Consequently, during transfer of the substrate, residual plating solution is less likely to oxidize, thereby preventing accompanying problems, including blackening of the surface of the plating layer. Therefore, when solder bumps are formed on the plating layer, the bonding strength between the plating layer and the solder is not lowered, and bonding reliability can be enhanced.
In the cooling means of the aforementioned plating apparatus, preferably, the cooling liquid is sprayed obliquely upward, and, when falling as a result of spraying, the cooling liquid is applied to the substrate from above the substrate, thus effecting cooling of the substrate. Therefore, since the sprayed cooling liquid is easily atomized in air, the cooling liquid can be uniformly applied to the substrate, to thereby cool the substrate uniformly.